| Rice can not only be used as the staple food of people,but rice flour can also be used as the ingredients of other foods.Whether rice or its flour,aging occurs in the storage process,resulting in deterioration of quality,and economic losses.However,the aging mechanism of rice is very complex,and there is no unified conclusion about it.During the aging process of rice,the change of starch composition is very small,and the change of non-starch composition——lipid and protein obviously affects the gelatinization of starch in rice.The outer layer of rice grains is rich in protein,and the outer layer of rice grains in storage is exposed to air,so it is an ideal material to research the aging changes.Therefore,this research took the protein-rich outer layer of rice grains(milling degree 15%)as the research object,and studied the effects of the outer protein of rice grains on starch gelatinization and its morphological mechanism by removing the lipid and various proteins in the outer powder of rice grains before and after storage.In order to reveal the effect of protein on starch gelatinization,we compared the differences between aged rice and fresh rice after protein removal.The main conclusions are as follows:(1)Effect of deproteinizing before storage on starch gelatinization and microscopic morphology.With fresh rice as raw material,through fresh rice grain of outer denudation grinding,according to the different solubility,one by one,removing lipid,albumin,globulin and glutelin and gliadin,then retrogradation(37?)12 months of storage,lipid and protein removal on starch gelatinization and the influence of microscopic morphology.The results showed that the difference of particle size distribution of the obtained residues disappeared between before and after aging with the removal of lipid and albumin in rice flour.The presence of albumin inhibited the disaggregation of starch granules,while the presence of lipid promoted the disaggregation of starch granules,and this effect became more obvious after aging.In the aging process,albumin and lipid contributed 118%and-18%to the difficulty of disaggregation of starch granules due to aging respectively,while globulin,glutelin and prolamin had little effect on it.The results of particle size analysis were supported by light microscope observation.Moreover,the presence of albumin in rice flour significantly reduced peak viscosity and breakdown,and increased pasting temperature after aging,indicating that the disaggregation difficulty of starch granules caused by albumin aging significantly changed pasting properties.Therefore,that the changes of albumin in rice flour during aging makes starch granule difficult to disaggregation is the main reason for the changes in pasting properties of rice flour after aging,which is of great significance to reveal the aging mechanism of rice flour.(2)Effect of deproteinizing after storage on starch gelatinization and microscopic morphology.The fresh rice was stored and aged at 37? for 12 months.The outer layers of rice grains were denudated and ground to remove lipid,albumin,globulin,gluten and gliadin one by one according to the different solubility.The effects of lipid and protein removal on starch gelatinization and microstructure were research.RVA gelatinization eigenvalue showed that lipid in aged rice increased PV;Albumin decreased PV and increased PaT.Globulin increased FV;Gluten decreased PV and increased PaT;Gliadin decreased PV and BD,and increased FV and PaT.The results showed that lipid in aged rice promoted the swelling of starch granules,while albumin,globulin,gluten and gliadin inhibited the swelling of starch granules and increased the energy required for gelatinization.The gelatinous texture of rice showed that the hardness,viscosity,masticability and adhesion of rice gelatine decreased gradually with the gradual removal of lipid and various proteins in aged rice.This indicated that the change of lipid and protein in aged rice was the main reason for the change of rice gelatinous structure.The results showed that the difference of particle size distribution of the obtained residues disappeared between before and after aging with the removal of lipid and albumin in rice flour.The presence of albumin inhibited the disaggregation of starch granules,while the presence of lipid promoted the disaggregation of starch granules,and this effect became more obvious after aging.In the aging process,albumin and lipid contributed 118%and-18%to the difficulty of disaggregation of starch granules due to aging respectively,while globulin,glutelin and prolamin had little effect on it.The results of particle size analysis were supported by light microscope observation.Moreover,the presence of albumin in rice flour significantly reduced peak viscosity and breakdown,and increased pasting temperature after aging,indicating that the disaggregation difficulty of starch granules caused by albumin aging significantly changed pasting properties.Therefore,that the changes of albumin in rice flour during aging makes starch granule difficult to disaggregation is the main reason for the changes in pasting properties of rice flour after aging,which is of great significance to reveal the aging mechanism of rice flour.(3)Effect of flour particle size on gelatinization behavior after aging.The fresh rice was crushed and screened into 9 grades according to particle size.After storage and aging,the effect of particle size of rice flour on gelatinization behavior after aging was investigated.RVA gelatinization characteristic values showed that PV and BD gradually increased,while HS,FV and PaT gradually decreased with the decrease of particle size in the range of 100 ?m?450 ?m after aging,which indicated that the swelling degree of starch particles increased with the decrease of particle size.When the particle size of rice flour decreased to 20?m?100?m,PV and BD decreased with the decrease of particle size,while HS,FV and PaT increased,which indicated that the cohesion between particle size was enhanced with the decrease of particle size,resulting in the swelling degree of starch particles decreased with the decrease of particle size.The results showed that the hardness,viscosity,masticability and adhesive properties of aged rice glue decreased with the decrease of rice flour particle size,which indicated that the particle size of aged rice flour was an important reason for the change of rice glue structure.The results of light microscopy showed that when the particle size was larger(100-450 ?m),the dispersion of old rice flour after gelatinization was less than that of fresh rice flour.When the particle size was small(20?100 ?m),there was no significant difference in morphology between the gelatinized aged rice flour and the fresh rice flour.These results indicate that the swelling degree of rice flour increases and the difficulty of separation between starch particles decreases with the decreasing particle size of rice flour(100-450 ?m)after aging.However,when the particle size of rice flour decreased to(20?100 ?m),the cohesion between grains increased,which resulted in the decrease of the swelling degree of rice flour,and the difficulty of starch dispersion among grains increased.In conclusion,protein is an important factor affecting the dispersion of starch particles in the aging process of rice.After aging,albumin,globulin and gluten significantly inhibit the dispersion of starch particles,thus affecting the gelatinization of starch and leading the deterioration of rice quality after aging.In this paper,through extracting lipid and proteins in rice grain outlayer and the preparation of rice flour with different particle size,RVA,texture,particle size distribution and morphology observation were used to research the effect of protein to starch gelatinization and its morphology mechanism,providing a new way to disclose rice aging mechanisms and a basis to retard rice aging and to reduce the loss of grain storage. |
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